The invention relates to a method for coating and bonding printed boards with tin by passing the printed boards through a bath of tin. The printed boards have areas immediately adjacent to one another and/or completely surrounded by conductor paths for which tinning is desired.
During this tinning process, due to the surface tension of the liquid tin, several undesirable effects might occur such as the bridging of neighboring conductor paths or the covering by solder bubbles of areas of fairly small dimensions which are surrounded by conductor paths. For example, such areas appear in printed boards employed for applying potential and provided with a network of intersecting conductor paths. In the case of wiring boards for rack back panels having a multiplicity of conductor paths, the number of such unwanted tin bubbles can be so large that a finishing operation is no longer economically justified. Such wiring boards are penetrated by pins, some of which might be bonded with the conductor paths and others of which might not be bonded. In the bonded pins, the hole is surrounded by a soldering terminal bonded to the conductor paths by connecting segments. The holes which are not bonded are located in the free areas between the conductor paths. However, if bubbles form in any of these areas, misbondings might occur between such areas and the conductor paths. During the tinning process, tin bubbles also might be formed that burst open prior to solidification and cause tin spillings that may likewise lead to misbondings.
It is an object of the invention to avoid both bridging and bubble formation between neighboring conductor paths.